This invention relates generally to imaging systems, and more particularly to imaging systems that use a retractor.
Some imaging systems such as nuclear medicine imaging systems having gamma cameras use a retractor as a transmission system to transmit power, signals and data between the imaging detectors and electronics used for processing, control and power. The retractor may also be referred to as a cable guidance system and allows a limited rotation span. For example, the rotor or rotating portion upon which the imaging detectors are mounted typically may be rotated more than one, but less than two full rotations in one or both of the clockwise (CW) and counter-clockwise (CCW) directions from a zero position. In contrast, a slip ring, such as those used by computed tomography (CT) and some gamma camera systems, allow unlimited rotations in both the CW and CCW directions.
Electronics track the rotating portion during normal use, such as by receiving rotation input from an absolute encoder, potentiometer, tooth wheel and flag and/or encoder combination, and the like. An angular read-out on a display and/or a warning when nearing the end of travel may be provided. End of travel microswitches have also been used to try to prevent the system from reaching or exceeding a travel limit. Mechanical devices such as hard stops have been used, but cannot safely stop heavy modern imaging detectors and may not be easily positioned to stop rotation at a position less than two full revolutions. If the tracking or corresponding display fails, such as during a power outage or computer or other component malfunction, an operator may not know if the retractor is nearing the end of travel. Moving the rotating portion beyond the end of travel, such as manually or by driving with a motor, may cause severe damage to the system. Specifically, the retractor may be damaged if the rotating portion travels beyond the designed travel limit.